U.S. patent number 9,813,190 [Application Number 15/200,924] was granted by the patent office on 2017-11-07 for pre-distortion calibration.
This patent grant is currently assigned to Intel IP Corporation. The grantee listed for this patent is Intel IP Corporation. Invention is credited to Roy Amel, Yuval Dafna, Roy Nahum, Ran Shimon, Ilan Sutskover, Tzahi Weisman.
United States Patent |
9,813,190 |
Sutskover , et al. |
November 7, 2017 |
Pre-distortion calibration
Abstract
Described herein are technologies related to an implementation
of a closed-loop system to measure and compensate non-linearity in
a transceiver circuitry of a device.
Inventors: |
Sutskover; Ilan (Hadera,
IL), Nahum; Roy (Beer Sheva, IL), Dafna;
Yuval (Raanana, IL), Shimon; Ran (Ramar Gan,
IL), Weisman; Tzahi (Mevaseret Tzion, IL),
Amel; Roy (Haifa, IL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Intel IP Corporation |
Santa Clara |
CA |
US |
|
|
Assignee: |
Intel IP Corporation (Santa
Clara, CA)
|
Family
ID: |
60189842 |
Appl.
No.: |
15/200,924 |
Filed: |
July 1, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
1/0042 (20130101); H04L 27/265 (20130101); H03F
3/24 (20130101); H03F 1/3247 (20130101); H04L
45/745 (20130101); H04L 7/0008 (20130101); H04L
43/028 (20130101); H04L 27/368 (20130101); H04L
25/03847 (20130101); H03F 2201/3233 (20130101) |
Current International
Class: |
H03H
7/40 (20060101); H04L 7/00 (20060101); H04L
12/741 (20130101); H04L 25/03 (20060101); H04L
1/00 (20060101); H04L 12/26 (20060101); H04L
27/26 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tran; Khanh C
Attorney, Agent or Firm: Schiff Hardin LLP
Claims
What is claimed is:
1. A method of performing pre-distortion calibration in a
transceiver of a device, the method comprising: estimating a linear
transfer function of a loopback signal to set coefficients of a
compensation filter, filtering, by the compensation filter, a
digital transmit signal, wherein the compensation filter is
configured to act as an echo canceller during the estimation of the
linear transfer function; comparing, by a Power Amplifier
Pre-Distortion (PAPD) analyzer, the loopback signal with the
filtered digital transmit signal; and configuring a PAPD Look-Up
Table (LUT) based on the comparison, wherein the PAPD LUT is for
implementing pre-distortion correction of subsequent data packets
to be transmitted.
2. The method of claim 1, further comprising: synchronizing, before
the estimating, by a synchronization block, the digital transmit
signal and the loopback signal for at least one of gain, phase, and
delay changes in data packets of the loopback signal.
3. The method of claim 1, further comprising: synchronizing, after
the filtering, by a synchronization block, the digital transmit
signal and the loopback signal for at least one of gain, phase, and
delay changes in data packets of the loopback signal.
4. The method as recited in claim 3, wherein the estimating and the
synchronizing occur at different time instants.
5. The method as recited in claim 3, wherein the estimating and the
synchronizing occur at a same data packet time.
6. The method as recited in claim 1, further comprising: training
the coefficients of the compensation filter to match a linear
portion at an input side of a power amplifier (PA), which is
coupled between the PAPD LUT and the PAPD analyzer, and a linear
portion at an output side of the PA.
7. The method as recited in claim 1, wherein the training is
performed while the PA is not operating.
8. The method as recited in claim 1, wherein the estimating of the
linear transfer function is performed during a low-transmit power
mode.
9. The method as recited in claim 1, further comprising: performing
any of the estimating, filtering, comparing, and configuring
iteratively.
10. The method as recited in claim 1, further comprising:
downconverting, by a baseband filter, the loopback signal to a
baseband loopback signal, wherein the comparing comprises comparing
the baseband loopback signal with the filtered digital transmit
signal.
11. The method as recited in claim 1, further comprising:
generating a control signal based on the comparison; and
configuring the PAPD LUT based on the control signal.
12. A method for evaluating transmit performance of a transceiver
of a device, the method comprising: receiving, by a synchronization
block, a Power Amplifier (PA) output signal via a loopback and a
filtered transmit signal; correcting, by the synchronization block,
data of the filtered transmit signal for at least one of phase,
gain and delay, wherein the filtered transmit signal is filtered by
a compensation filter, and assessing, by a performance assessor,
transmit performance of the corrected, filtered transmit signal,
wherein the performance assessor comprises at least one of an Error
Vector Magnitude (EVM) meter, a mask meter, and an Adjacent Channel
Leakage Ratio (ACLR) meter, wherein the transmit performance is
used to control a parameter of subsequent data to be
transmitted.
13. The method as recited in claim 12, wherein the controlled
parameter is transmit power.
14. A method for evaluating transmit performance of a transceiver
of a device, the method comprising: receiving, by a synchronization
block, a Power Amplifier (PA) output signal via a loopback and a
filtered transmit signal; correcting, by the synchronization block,
data of the filtered transmit signal for at least one of phase,
gain and delay, wherein the filtered transmit signal is filtered by
a compensation filter; and assessing, by a performance assessor,
transmit performance of the corrected, filtered transmit signal,
the transmit performance being used to control a parameter of
subsequent data to be transmitted, wherein the controlled parameter
is an offset in pre-distortion look-up table entries.
15. A device, comprising: a compensation filter configured to
filter a digital transmit signal, wherein a Fast Fourier Transform
(FFT) engine is configured to estimate a linear transfer function
of a loopback signal to set coefficients of the compensation
filter, a Power Amplifier Pre-Distortion (PAPD) analyzer coupled to
the compensation filter and configured to compare the loopback
signal with the filtered digital transmit signal; and a PAPD
Look-Up Table (LUT) configured based on the comparison, wherein the
PAPD LUT is for implementing pre-distortion correction of
subsequent data packets to be transmitted.
16. The device of claim 15, further comprising: a synchronization
block configured to, before the estimating, synchronize the digital
transmit signal and the loopback signal for at least one of gain,
phase, and delay changes in data packets of the loopback
signal.
17. The device of claim 15, further comprising: a synchronization
block configured to, after the filtering, synchronize the digital
transmit signal and the loopback signal for at least one of gain,
phase, and delay changes in data packets of the loopback
signal.
18. The device as recited in claim 17, wherein the PAPD analyzer
comprises: a binning block configured to generate an input-output
curve based on the synchronized signals, a post-processing block is
configured to generate a control signal based on a non-linearity
derived from the input-output curve, wherein the PAPD LUT is
configured based on the control signal.
19. The device as recited in claim 17, wherein the synchronization
block is further configured to emulate and/or correct gain, phase,
and/or delay.
20. The device as recited in claim 15, wherein the compensation
filter is a Finite Impulse Response (FIR) filter, and the
coefficients comprise complex coefficients.
21. The device as recited in claim 15, wherein the PAPD analyzer
comprises: a post processing block configured to generate a control
signal based on the comparison, wherein the PAPD LUT is configured
based on the control signal.
22. The device as recited in claim 15, wherein the FFT engine is
configured to estimate the linear transfer function during a low
transmit-power mode.
23. A device as recited in claim 15, further comprising: a transmit
chain comprising a digital-to-analog converter and an analog Power
Amplifier (PA), and configured to receive the transmit signal; a
loopback receive chain coupled to an output of the PA, and
comprising an analog-to-digital converter, wherein the PAPD
analyzer is coupled to an output of the loopback receive chain, and
a compensation filter is digital and coupled between a PAPD
analyzer and the transmit chain, and wherein a synchronization
block is configurable to correct instantaneous changes in data of a
specific transmit signal prior to comparing the loopback signal
with the specific transmit signal.
Description
BACKGROUND
An increasing number of wireless communication standards and a
trend towards ever smaller, slimmer and lighter devices may cause
design challenges for a device's transceiver circuitry. The design
challenges may relate to reduction of noise, jitters, etc. during
receiving or transmitting operations.
A closed-loop system may be used to reduce the noise, jitters, etc.
The closed-loop system may employ a loopback signal that may be
taken from an output of a power amplifier (PA) in order to control
transmission that may be required in wireless platforms using
on-line rather than production line calibrations.
The implementations described herein address the measurement and
compensation of non-linearity in the transceiver circuitry.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a perspective diagram of a communication system
in accordance with an aspect of the disclosure.
FIG. 2 illustrates a schematic diagram of a closed-loop system
configured to measure and compensate non-linearity in a transceiver
circuitry of a device in accordance with an aspect of the
disclosure.
FIG. 3 illustrates a schematic diagram of a system configured to
measure and correct non-linearity in accordance with an aspect of
the disclosure.
FIG. 4 illustrates a flowchart of a process for implementing a
closed-loop system for measuring and compensating non-linearity in
a device in accordance with an aspect of the disclosure.
DETAILED DESCRIPTION
Described herein is a technology for implementing a closed-loop
system configured to measure and compensate for non-linearity in a
transceiver circuitry of a device.
For example, a linear transfer function of the closed-loop system
is first estimated, for example, during an initial low
transmit-power data packet transmission (low transmit-power mode)
when the transmission is low enough so that only a linear response
is captured. With low transmit power, the power amplifier response
is relatively linear. A compensation filter, which may be a real or
complex filter, is configured so that the filter emulates the
linear transfer function of the loopback signal. When an output of
the real loopback signal and of the compensation filter output
filter are observed, there is essentially only the nonlinearity of
a power amplifier that distinguishes between the two signals.
At a subsequent time instant, a measurement and
correction/synchronization of instantaneous changes in gain, phase,
and/or delay of a data packet is performed, for example, through a
synchronization block. After the correction of the instantaneous
changes of the data packet by the synchronization block, a Power
Amplifier Pre-Distortion (PAPD) analyzer of the closed-loop system
may be configured to compare a baseband signal of a loopback signal
and an original baseband signal of a reference transmit signal. The
loopback signal as described herein may include the signal that is
sampled from an output of a transmit chain and passes through a
receive chain. The reference transmit signal is also the input
signal.
After the comparison by the PAPD analyzer, firmware from a
post-processing block reads the comparison results from the PAPD
analyzer and sets a PAPD Look-Up Table (LUT) to perform
pre-distortion corrections on subsequent data packets to be
transmitted. The firmware, for example may generate a control
signal for the PAPD LUT to perform the pre-distortion
corrections.
As described herein, an echo cancellation may be further
implemented prior to, or during the emulation of the linear
transfer function by the compensation filter. For example, prior to
the emulation of the linear transfer function, the compensation
filter may be further configured to initially perform echo
cancellation in order to minimize and/or cancel signal leakages
from an input side of the transmit chain to the loopback signal. In
another example, the emulation of the linear transfer function may
include the echo cancellation.
FIG. 1 illustrates a perspective diagram of a communication system
100 in accordance with an aspect of the disclosure. The system 100
comprises a device 102 with an antenna 104, and another device 106
with an antenna 108.
The devices 102 or 106 may include, but is not limited to,
non-portable devices such as an access point (AP), non-portable
computers, and the like; and portable devices such as a tablet
computer, a netbook, a notebook computer, a laptop computer, mobile
phone, a cellular phone, a smartphone, a personal digital
assistant, a multimedia playback device, a digital music player, a
digital video player, a navigational device, a digital camera, and
the like.
The device 102, for example, may communicate with the other device
106 in a network environment. The network environment, for example,
includes a cellular base station configured to facilitate
communications between the device 102 and the other device 106. In
another example, the device 102 communicates with the access point
(AP), or vice-versa, using for example, wireless fidelity (Wi-Fi)
orthogonal frequency division multiplexing (OFDM) data packets, or
other kinds of modulation technique(s). In both of these examples,
a non-linearity detection, measurement, and compensation as
described in present implementations herein may be applied by the
device 102 or 106.
For example, a reference transmit signal is initially transmitted
at low power to obtain linear state or linear transfer function of
the transceiver circuitry (not shown) of the device 102. At this
condition, the linear transfer function of the transceiver
circuitry is estimated to set coefficients of a compensation filter
(not shown) in the transceiver circuitry.
At another time instant (i.e., after the estimation of the linear
transfer function), the synchronization block ensures that the
loopback signal and the reference transmit signal match in gain,
phase, and/or delay. The change in gain, phase and/or delay may be
applied to the loopback signal or the reference transmit signal.
However, the estimation of the loopback signal linear transfer
function is performed on the reference transmit signal and not the
loopback signal; otherwise, the loopback channel would need to be
inverted.
With the estimated linear transfer function, and corrected
instantaneous changes in the gain, phase, and/or delay of the data
packets, a PAPD analyzer (not shown) in the device 102 or 106 may
be configured to measure non-linearity from the loopback signal by
comparing a loopback baseband signal with a baseband signal of the
reference transmit signal. Thereafter, the PAPD analyzer may return
either the non-linearity or the look-up table (LUT) of the
non-linearity. In the case the PAPD analyzer returns the
non-linearity, some other entity (e.g., firmware or digital signal
processor) may be required to perform calculations to deduce the
pre-distortion tables associated therewith.
In other implementations, an initial echo cancellation may be
performed at the transceiver circuitry in order to minimize and/or
cancel signal leakages. For example, the estimation of the linear
transfer function of the transceiver circuitry may further include
the cancellation of the signal leakages. In this example, the echo
cancellation may be implemented during the initial calibration
process i.e., prior to estimation of the linear transfer function
of the loopback signal.
The example arrangement 100 illustrates in a limited manner basic
components of wired/wireless communications between the devices 102
and 106, other components such as battery, one or more processors,
SIM card, etc. were not described in order to simplify the
embodiments described herein
FIG. 2 illustrates a schematic diagram of a closed-loop system 200
configured to implement measurement and compensation of
transmission non-linearity in the transceiver circuitry of the
device 102 in accordance with an aspect of the disclosure.
As shown, the system 200 includes a transmit chain 202, a receive
chain 204, an optional directional coupler 206, a compensation
filter 208, a PAPD analyzer 210, and a power amplifier
pre-distortion (PAPD) look-up table (LUT) 212 (also known as a
Digital Pre-Distortion (DPD) LUT). The transmit chain 202 may
further include, but not be limited to, a digital-to-analog
converter (D2A) 214, a transmit (Tx) filter 216, a transmitter
mixer 218, and an analog power amplifier (PA) 220. The receive
chain 204 may further include, but not be limited to, receiver
mixer 222, a receiver baseband filter 224, an analog-to-digital
converter (A2D) 226 and a receiver digital processor 228. The
receiver baseband filter 224 is configured to downconvert a radio
frequency or intermediate frequency to baseband.
The apparatus 200 further shows an input signal 230 that may
represent an original signal to be transmitted or is referred to
herein as the reference transmit signal; an output signal 232 that
may represent an output of the transmit chain 202 or the analog PA
220; a receive signal 234 that may represent a sampled transmit
signal from the optional directional coupler 206 or a large
attenuator; a loopback signal 236 that may include a loopback
baseband signal with a non-linearity that is analyzed by the PAPD
analyzer 210; and a control signal 238 that is generated by a
firmware based on non-linearity analysis from the PAPD analyzer
210. The control signal 238, for example, is used to set up
parameters of the PAPD LUT 212 in order to correct the
non-linearity in the loopback baseband signal or the loopback
signal 236. In this example, a reading of non-linearity analysis
and setting up of the PAPD LUT 212 by the firmware may be
implemented offline.
As a general overview of the apparatus 200 operation, the input
signal 230 may be first transmitted at a low transmit-power mode
i.e., the firmware facilitates transmit power-adjustment of the
input signal 230 (or the reference transmit signal). The low
transmit-power mode is not limited to the transmit power-adjustment
from a Digital Signal Processor (DSP) or modem (not shown), but may
also include power-gain adjustment of the analog PA 220, power
adjustment of a configurable baseband amplifier (not shown) that
may be disposed between the D2A 214 and mixer 218, and the like.
Obtaining good linearity may be accomplished by reducing power of
the input signal 230, preferably before it is amplified.
In an implementation, the compensation filter 208 may be disposed
at the transmit side between an input side of the PAPD LUT 212 and
the PAPD analyzer 210, while the measurements and corrections of
the instantaneous changes on the data packet of the reference
transmit signal may be implemented at the loopback signal side
e.g., at the receive chain side. In other implementations, the
compensation filter 208 may become an equalizer filter implemented
at the loopback signal side, while the measurements and corrections
of the instantaneous changes on the data packet of the reference
transmit signal may be implemented at the transmit side.
Alternatively, the compensation filter 208 and the measurements and
corrections of the instantaneous changes on the data packet of the
reference transmit signal may both be implemented at either the
transmit side or the loopback signal side, e.g., at the receive
chain side.
At the low transmit-power mode, the combined linear transfer
functions of the transmit chain 202 and the loopback receive chain
204 is estimated and the coefficients of the compensation filter
208, which may be a Finite Impulse Response (FIR) filter are
changed accordingly. The coefficients are complex, where real
filters are a special case of complex filters. Furthermore, a
synchronization block 304, as further discussed below with respect
to FIG. 3, may measure and correct instantaneous changes in data
packets of the reference transmit signal (or alternatively, the
loopback signal).
At the low transmit-power mode, the coefficients of the
compensation filter 208 are trained to match linear portions at an
input side (i.e., pre-PA) and output side (i.e., post-PA) of the
analog PA 220. That is, the transfer function of the transmit chain
202 and the receive chain 204 is assumed to be linear at the low
transmit-power mode. To this end, the linear transfer function is
captured and trained as coefficients of the compensation filter
208. Optionally, that training may be performed by transmitting a
data packet of the reference transmit signal through the PA 220
while it is shut-down.
The comparison of the loopback signal 236 and the reference
transmit signal 230 may be performed by capturing data sequences
into memory and reusing the device's 102 Fast Fourier Transform
(FFT) engine to calculate a frequency response by dividing the FFT
output of a first reference transmit signal data sequence by a FFT
output of a second reference transmit signal data sequence. A
smoothing operation is then applied to the divided signal, which is
the estimated channel frequency response. The divided signal may
then be transformed back to the time domain using an inverse FFT
(iFFT) or FFT engine, and then the coefficients of the compensation
filter 208 may be formed by multiplying by a configurable
window.
Thereafter, the PAPD analyzer 210 compares the loopback baseband
signal of the loopback signal 236 with the baseband signal of the
reference transmit signal that passed through the compensation
filter 208. Based on this comparison that is read by the firmware,
the firmware generates the control signal 238 to set up the PAPD
LUT 212 for pre-distortion correction of subsequent data packets to
be transmitted.
At another time instant, the synchronization block 304--which may
be a part of the PAPD analyzer 210--may measure and correct the
instantaneous changes of phase, gain, and/or delay between data
packets of the reference transmit signal (i.e., Tx signal 318 in
FIG. 3) and the loopback signal 236. For example, a possible
temperature change may generate a change in phase and/or gain of
the data packets of the reference transmit signal or input signal
230. In another example, a possible digital sync First-In-First-Out
(sync-FIFO) may generate differences in instantaneous delay of the
data packets. Although the impairments in both examples are
relatively small, they are treated herein as significant with
regard to non-linearity measurements by the PAPD analyzer 210. As
such, the matching of the phase, gain, and/or delay between data
packets of the reference transmit signal 230 and the loopback
signal 236 are implemented prior to the measurement of
non-linearity through the PAPD analyzer 210.
The PAPD LUT 212 may be disposed prior to the transmit chain 202.
Furthermore, the PAPD LUT 212 may be configured to perform
non-linear pre-distortion corrections on the subsequent data packet
transmissions. For example, on the subsequent transmission of
particular data packets, the parameters of the PAPD LUT 212 may
transform the particular data packets into a desired output such as
an output signal 232 less the non-linearity as previously measured
through the PAPD analyzer 210.
In other implementations, the compensation filter 208 may be
further configured to act as an echo canceller to the input signal
230 that may leak into the loopback signal 236. That is, prior to
the emulation by the compensation filter 208 and the correction of
the instantaneous changes in gain, phase and delay by the
synchronization block 304, the signal leakage may occur as well. As
such, the initial configuration of the compensation filter 208 may
include echo cancellation.
FIG. 3 is a schematic diagram of a system 300 configured to measure
and correct non-linearity in accordance with an aspect of the
disclosure.
As shown, there is an input signal 230, the PAPD LUT 212, a
non-linear block 302 that may represent the transmit chain 202 and
receive chain 204 during pre-distortion correction, and the PAPD
analyzer of FIG. 2. The PAPD analyzer 210 comprises a
synchronization block 304, a performance assessment meter 306, a
binning block 308, a post-processing block 310, and a multiplexer
(MUX) 312. The synchronization block 304 comprises a channel
learning 341, integer delay learning 343, fractional delay learning
342, a loopback equalizing filter 344 which is the compensation
filter 208, fractional delay compensator 345 that may be
implemented by a variable rate converter (VRC), and an integer
delay compensator 346. The integer delay compensator 346 may be
implemented as a tap delay line.
Furthermore, the MUX 312 is configured to select between a pre-PAPD
LUT signal 314 or a post-PAPD LUT signal 316. Furthermore still,
there is a transmit (Tx) signal 318, which is representative of the
reference transmit signal, the loopback signal 236, a transmit
buffer 320, and a receive buffer 322.
As described herein, the loopback equalizing filter 344 may emulate
the linear transfer function at the transmit and receive side at
low transmit-power mode as discussed above, and the training of
coefficients of the loopback equalizing filter 344 is implemented
online using real packets at the end-user. With this emulation, the
synchronization block 304 is configured to ensure that the Tx
signal 318 (i.e., reference transmit signal) is matched to the
loopback signal 236 without differences in gain, phase, and/or
delay. This synchronization activity may be performed iteratively,
such as twice. That is, after impairments are corrected, the
impairments are measured and corrected again to achieve better
performance, and subsequently apply a binning or the EVM
measurement, for example.
Thereafter, the binning block 308 may collect corrected signals
from the synchronization block 304 and generate an input-output
curve where the Tx signal 318 may be the input (signal) while the
loopback signal 236 may be the output (signal). For example, if the
post-PAPD LUT signal 316 is collected by the binning block 308 as
the input, then the input-output curve may reflect non-linear
portions of the loopback signal 236. The post-PAPD LUT signal 316
may include the input signal 230 that undergoes pre-distortion
correction through the PAPD LUT 212 while the pre-PAPD LUT signal
314 may include the input signal 230 without pre-distortion
correction by the PAPD LUT 212.
With continuing reference to FIG. 3, the binning block 308 is
configured to generate an input-output nonlinearity curve. The
post-processing block 310 is configured to invert the nonlinearity
curve, that is, calculate the pre-distortion correction for the
PAPD LUT 212.
The performance assessment meter 306 may be an Error Vector
Magnitude (EVM) meter, a mask meter and/or an Adjacent Channel
Leakage Ratio (ACLR) meter or out-of-band emission meter. The EVM
is measured based on a comparison of two output signals 332 and 334
from the synchronization block 304, that is, Tx signal 332
associated with Tx signal 318 and receive (Rx) signal 334
associated with loopback signal 236. The EVM measurement may then
be used to verify that the input signal is still high quality,
retrigger the closed loop PAPD flow, or lower the transmit power so
that the EVM is improved.
At the synchronization block 304, the channel learning 341 is
configured to capture the linear portions of the transmit chain 202
and the receive chain 204 and thereafter, the coefficients of the
FIR filter, which is represented by the loopback equalizing filter
344, are adjusted to match the captured linear transfer function.
Furthermore, the channel learning 341 may facilitate measurement
and correction of instantaneous changes in the phase and/or gain of
the data packets of the Tx signal 318.
In order to maintain size of the FIR filter, the integer delay
learning 343 and the integer delay compensator 346 are implemented
to emulate a large delay, for example, of the Tx signal 318
compared with the loopback signal 236. The estimated large delay is
digitally placed so that the size of the FIR filter need not be
increased and thus, a shorter FIR filter may be used. On the other
hand, the fractional delay learning 342 and the fractional delay
compensator 345 may be implemented to correct for small delays due
to FIFO feature of transmitting data packets. The fractional delay
is also applied during the channel learning. If the FIR filter is
well located in the time domain, the FIR filter's length may be
significantly shorter than trying to capture the fractional delay
by the FIR filter itself. Therefore, there is compensation for
integer delay and fractional delay at the same (low-power) packet
used to train the compensation filter 208, and then in a next
(high-power) packet, because of the sync-FIFO feature the
fractional delay is compensated again. This synchronization
correction before training is optional but recommended to reduce
cost.
The transmission signal quality assessment, by comparing the
loopback signal 236 to with the reference transmit signal for
measuring parameters such as EVM, ACLR and mask, rely on the
visibility of the transmission signal with the elimination of the
linear and delay distortions. Based on signal quality assessment,
the system 200 may choose to react, for example, by lowering
transmit power, adjusting other parameters, and/or
re-calibrating.
FIG. 4 illustrates a flowchart 400 of a method for implementing a
closed-loop system for measuring and compensating non-linearity in
a transceiver circuitry of a device in accordance with an aspect of
the disclosure. The order in which the method is described is not
intended to be construed as limiting, and any number of the
described method blocks may be combined in any order to implement
the method, or an alternative method. Additionally, individual
blocks may be deleted from the method without departing from the
spirit and scope of the subject matter described herein.
Furthermore, the method may be implemented in any suitable
hardware, software, firmware, or a combination thereof, without
departing from the scope of the disclosure.
At block 402, estimating a linear transfer function of a
transceiver circuitry to set coefficients of the compensation
filter 208 is performed. For example, a reference transmit signal
or input signal 230 is transmitted at low transmit-power mode
through a firmware power adjustment at the input signal 230 side;
or through a power gain-adjustment of the TX chain 202. In this
example, the linear transfer function of the transmit chain 202 and
the receive chain 204 is emulated. More specifically, coefficients
of the compensation filter 208 are trained to match linear portions
at an input side (i.e., pre-PA) and output side (i.e., post-PA) of
the analog PA 220.
In other implementations, the compensation filter 208 is configured
to act as an echo canceller for the input signal 230 that may leak
into the receive chain 204, and into the loopback signal 236. In
this other implementation, the echo cancellation is implemented
prior to the emulating of the linear transfer function of the
transceiver circuitry.
At block 404, measuring and correcting instantaneous changes on a
data packet of a reference transmit signal is performed. For
example, the synchronization block 304 measures and corrects the
instantaneous difference or changes in the gain, phase, and/or
delay of a particular data packets. In this example, the first few
data packets are used by the synchronization block 304 to measure
and correct the instantaneous changes of the gain, phase, and/or
delay.
At block 406, non-linearity of the loopback signal 236 is measured.
The nonlinearity may be determined by the binning block 308
comparing the Tx signal 332 and Rx signal 334 from the
synchronization block 304 and generating the input-output
nonlinearity curve.
At block 408, the PAPD LUT 212 is configured for pre-distortion
corrections on subsequent data packet transmission based upon the
comparison between the loopback signal 236 and the reference
transmit signal. For example, the firmware reads the non-linearity
from the measurements made by the PAPD analyzer 210 and based from
this non-linearity, firmware facilitates the setting up of the PAPD
LUT 212 to be applied to subsequent data packets to be transmitted.
In this example, the PAPD LUT 212 is configured to perform
pre-distortion correction of the transmit chain 202 and in
particular the analog PA 220.
In other implementations, the PAPD analyzer 210 generates a control
signal 238 that is received and used by the PAPD LUT 212 for
pre-distortion correction of the transceiver circuitry.
Example 1 is a method of performing pre-distortion calibration in a
transceiver of a device, the method comprising: estimating a linear
transfer function of a loopback signal to set coefficients of a
compensation filter; filtering, by the compensation filter, a
digital transmit signal; comparing, by a Power Amplifier
Pre-Distortion (PAPD) analyzer, the loopback signal with the
filtered digital transmit signal; and configuring a PAPD Look-Up
Table (LUT) based on the comparison, wherein the PAPD LUT is for
implementing pre-distortion correction of subsequent data packets
to be transmitted.
In Example 2, the subject matter of Example 1, further comprising:
synchronizing, before the estimating, by a synchronization block,
the digital transmit signal and the loopback signal for at least
one of gain, phase, and delay changes in data packets of the
loopback signal.
In Example 3, the subject matter of Example 1, further comprising:
synchronizing, after the filtering, by a synchronization block, the
digital transmit signal and the loopback signal for at least one of
gain, phase, and delay changes in data packets of the loopback
signal.
In Example 4, the subject matter of Example 3, wherein the
estimating and the synchronizing occur at different time
instants.
In Example 5, the subject matter of Example 3, wherein the
estimating and the synchronizing occur at a same data packet
time.
In Example 6, the subject matter of Example 1, further comprising:
training the coefficients of the compensation filter to match a
linear portion at an input side of a power amplifier (PA), which is
coupled between the PAPD LUT and the PAPD analyzer, and a linear
portion at an output side of the PA.
In Example 7, the subject matter of Example 1, wherein the training
is performed while the PA is not operating.
In Example 8, the subject matter of Example 1, wherein the
estimating of the linear transfer function is performed during a
low-transmit power mode.
In Example 9, the subject matter of Example 1, further comprising:
performing any of the estimating, filtering, comparing, and
configuring iteratively.
In Example 10, the subject matter of Example 1, wherein the
compensation filter is configured to act as an echo canceller
during the estimation of the linear transfer function.
In Example 11, the subject matter of Example 1, further comprising:
downconverting, by a baseband filter, the loopback signal to a
baseband loopback signal, wherein the comparing comprises comparing
the baseband loopback signal with the filtered digital transmit
signal.
In Example 12, the subject matter of Example 1, further comprising:
generating a control signal based on the comparison; and
configuring the PAPD LUT based on the control signal.
Example 13 is a method for evaluating transmit performance of a
transceiver of a device, the method comprising: receiving, by a
synchronization block, a Power Amplifier (PA) output signal via a
loopback and a filtered transmit signal; correcting, by the
synchronization block, data of the filtered transmit signal for
phase, gain and/or delay, wherein the filtered transmit signal is
filtered by a compensation filter; and assessing, by a performance
assessor, transmit performance of the corrected, filtered transmit
signal, wherein the transmit performance is used to control a
parameter of subsequent data to be transmitted.
In Example 14, the subject matter of Example 13, wherein the
performance assessor comprises at least one of an Error Vector
Magnitude (EVM) meter, a mask meter, and an Adjacent Channel
Leakage Ratio (ACLR) meter.
In Example 15, the subject matter of Example 13, wherein the
controlled parameter is transmit power.
In Example 16, the subject matter of Example 13, wherein the
controlled parameter is an offset in pre-distortion look-up table
entries.
Example 17 is a device, comprising: a compensation filter
configured to filter a digital transmit signal, wherein a Fast
Fourier Transform (FFT) engine is configured to estimate a linear
transfer function of a loopback signal to set coefficients of the
compensation filter; a Power Amplifier Pre-Distortion (PAPD)
analyzer coupled to the compensation filter and configured to
compare the loopback signal with the filtered digital transmit
signal; and a PAPD Look-Up Table (LUT) configured based on the
comparison, wherein the PAPD LUT is for implementing pre-distortion
correction of subsequent data packets to be transmitted.
In Example 18, the subject matter of Example 17, further
comprising: a synchronization block configured to, before the
estimating, synchronize the digital transmit signal and the
loopback signal for at least one of gain, phase, and delay changes
in data packets of the loopback signal.
In Example 19, the subject matter of Example 17, further
comprising: a synchronization block configured to, after the
filtering, synchronize the digital transmit signal and the loopback
signal for at least one of gain, phase, and delay changes in data
packets of the loopback signal.
In Example 20, the subject matter of Example 19, wherein the PAPD
analyzer comprises: a binning block configured to generate an
input-output curve based on the synchronized signals, a
post-processing block is configured to generate a control signal
based on a non-linearity derived from the input-output curve,
wherein the PAPD LUT is configured based on the control signal.
In Example 21, the subject matter of Example 19, wherein the
synchronization block is further configured to emulate and/or
correct gain, phase, and/or delay.
In Example 22, the subject matter of Example 17, wherein the
compensation filter is a Finite Impulse Response (FIR) filter, and
the coefficients comprise complex coefficients.
In Example 23, the subject matter of Example 17, wherein the PAPD
analyzer comprises: a post processing block configured to generate
a control signal based on the comparison, wherein the PAPD LUT is
configured based on the control signal.
In Example 24, the subject matter of Example 17, wherein the FFT
engine is configured to estimate the linear transfer function
during a low transmit-power mode.
In Example 25, the subject matter of Example 17, further
comprising: a transmit chain comprising a digital-to-analog
converter and an analog Power Amplifier (PA), and configured to
receive the transmit signal; a loopback receive chain coupled to an
output of the PA, and comprising an analog-to-digital converter;
wherein the PAPD analyzer is coupled to an output of the loopback
receive chain, and the compensation filter is digital and coupled
between the PAPD analyzer and the transmit chain, and wherein the
synchronization block is configurable to correct instantaneous
changes in data of a specific transmit signal prior to comparing
the loopback signal with the specific transmit signal.
Example 26 is a device, comprising: a compensation filter means for
filtering a digital transmit signal, wherein a Fast Fourier
Transform (FFT) engine means is for estimating a linear transfer
function of a loopback signal to set coefficients of the
compensation filter means; a Power Amplifier Pre-Distortion (PAPD)
analyzing means coupled to the compensation filter and for
comparing the loopback signal with the filtered digital transmit
signal; and a PAPD Look-Up Table (LUT) means configured based on
the comparison, wherein the PAPD LUT means is for implementing
pre-distortion correction of subsequent data packets to be
transmitted.
In Example 27, the subject matter of Example 26, further
comprising: a synchronization means for, before the estimating,
synchronizing the digital transmit signal and the loopback signal
for at least one of gain, phase, and delay changes in data packets
of the loopback signal.
In Example 28, the subject matter of Example 26, further
comprising: a synchronization means for, after the filtering,
synchronizing the digital transmit signal and the loopback signal
for at least one of gain, phase, and delay changes in data packets
of the loopback signal.
In Example 29, the subject matter of Example 28, wherein the PAPD
analyzing means comprises: a binning means for generating an
input-output curve based on the synchronized signals, a
post-processing means for generating a control signal based on a
non-linearity derived from the input-output curve, wherein the PAPD
LUT means is configured based on the control signal.
In Example 30, the subject matter of Example 28, wherein the
synchronization means is further for emulating and/or correct gain,
phase, and/or delay.
In Example 31, the subject matter of Example 26, wherein the
compensation filter means is a Finite Impulse Response (FIR)
filter, and the coefficients comprise complex coefficients.
In Example 32, the subject matter of Example 26, wherein the PAPD
analyzing means comprises: a post processing means for generating a
control signal based on the comparison, wherein the PAPD LUT means
is configured based on the control signal.
In Example 33, the subject matter of Example 26, wherein the FFT
engine is for estimating the linear transfer function during a low
transmit-power mode.
In Example 34, the subject matter of Example 26, further
comprising: a transmit chain comprising a digital-to-analog
converting means and an analog Power Amplifier (PA), and configured
to receive the transmit signal; a loopback receive chain coupled to
an output of the PA, and comprising an analog-to-digital converting
means; wherein the PAPD analyzing means is coupled to an output of
the loopback receive chain, and the compensation filter means is
digital and coupled between the PAPD analyzing means and the
transmit chain, and wherein the synchronization means is
configurable to correct instantaneous changes in data of a specific
transmit signal prior to comparing the loopback signal with the
specific transmit signal.
Example 36 is an apparatus as substantially shown and
described.
Example 37 is a method as substantially shown and described.
While the foregoing has been described in conjunction with
exemplary aspect, it is understood that the term "exemplary" is
merely meant as an example, rather than the best or optimal.
Accordingly, the disclosure is intended to cover alternatives,
modifications and equivalents, which may be included within the
scope of the disclosure.
Although specific aspects have been illustrated and described
herein, it will be appreciated by those of ordinary skill in the
art that a variety of alternate and/or equivalent implementations
may be substituted for the specific aspects shown and described
without departing from the scope of the present application. This
application is intended to cover any adaptations or variations of
the specific aspects discussed herein.
* * * * *